The present invention relates to a semiconductor device, a receiver, a transmitter, a transceiver, and a communication system, and more particularly to a semiconductor device, a receiver, a transmitter, a transceiver, and a communication system having a function for transmitting/receiving data in synchronization with a clock signal.
In recent years, a serial digital transmission system is used in many cases for communications between devices coupled to a communication network system and for data exchanges inside a personal computer. In a serial digital transmission system, serial signals are exchanged at high speed between semiconductor devices.
In a serial digital transmission system, a data signal is transmitted with a clock signal superimposed thereon and, on the receiving side, the clock signal synchronized with the data signal is reproduced using a clock and data recovery circuit. When, for data exchanges between semiconductor devices, high-speed digital signals are used (based on a serial digital transmission system), effects of harmonics of digital signals become conspicuous.
Harmonics of a digital signal can cause, as unwanted radiation noise, various problems. For example, unwanted radiation noise superimposed on a communication channel can cause communication failure. Unwanted radiation noise can also cause audio and video quality deterioration in electronic devices such as radios and TVs.
Hence, an SSCG (Spread Spectrum Clock Generator) is used to reduce unwanted radiation noise by slightly shifting the frequency of a clock signal used in a serial digital transmission system from the peak of an oscillation frequency so as not to fix the clock signal to a single frequency.
In Japanese Unexamined Patent Publication No. 2011-041121, a transceiver provided with a PLL circuit which corrects a transmit clock signal using the difference between the frequency of receive data (data received) and the frequency of an operation clock signal is disclosed. Also, the transceiver disclosed in Japanese Unexamined Patent Publication No. 2011-041121 includes an SSCG so as to reduce unwanted radiation noise generated from data received and transmitted.